Despite the high rate of sudden death in the first 2 months following a myocardial infarction (Ml), current guidelines for implantable cardioverter defibrillators (ICDs) recommend delayed implantation (>40 days) after an Ml in patients with low ejection fraction (EF). Delaying implantation leaves an unprotected window of increased sudden death risk prior to ICD implantation. In addition, only left ventricular ejection fraction (EF) is used to decide whether a post-Mi patient should subsequently receive an ICD for primary prevention of sudden death. In this setting, only 20% of patients will have spontaneous ventricular arrhythmias requiring ICD shocks in the next 5 years. A more cost-effective method for selecting patients for primary prevention ICD implantation is needed. To address these two deficiencies, we propose the Vest prevention of Early Sudden death Trial (VEST) and the PREDiction of ICd Therapies Study (PREDICTS). This proposal seeks funding for a Clinical Coordinating Center, the linked R01 (PI Hulley) is for a Data Coordinating Center, and the remaining funding (80%) will come from industry. VEST is a multicenter, randomized, controlled trial to determine whether a non-invasive wearable defibrillator vest will reduce overall mortality during the first 60 days following an Ml in patients with left ventricular dysfunction (EF<35%). PREDICTS is a follow-up to this randomized intervention, in which participants in VEST will undergo a battery of risk stratification tests including T wave alternans, baroreflex sensitivity, Holter monitoring and 7 other likely predictors before placement of an ICD. Participants will then be monitored for ICD shocks and other clinical outcomes over the next 5 years. These data will be used to develop and validate a multivariable risk stratification tool that predicts the occurrence of "shockable" ventricular arrhythmias and efficiently identifies high-risk patients in whom an ICD would be most cost-effective (and low-risk patients in whom an ICD is not necessary). Biological samples and data from both studies will be stored and made available to outside investigators for future studies. We anticipate that VEST and PREDICTS will have a major impact on the 500,000 annual sudden deaths in the US by testing an intervention that may protect the very highest-risk early post-Mi patients, and by identifying a risk stratification strategy to identify those at highest and lowest risk and make ICD implantation more cost-effective.